1. Field of the Invention
The present invention relates to a brushless electric signal transmission device, and more specifically to an improvement in a brushless electric signal transmission device for transmitting/receiving electric signals between a fixed body and a rotatable body reciprocatively (clockwise or counterclockwise) rotated within a predetermined number of rotations, which is suitable for use in a steering apparatus for an automotive vehicle, for instance.
2. Description of the Prior Art
FIGS. 1(a) and 1(b) shows an example of prior-art brushless electric signal transmitting device, in which a rotatable body (i.e. cylindrical rotor) 101 is rotatably disposed at a center of a fixed body (i.e. hollow cylindrical housing) 102 concentrically to each other with an annular space between the two. Within this space, a flexible electric wiring member 103 is wound by plural turns around the outer circumference of the rotor 101, and an inner end of the wiring member 103 is fixed to the rotor 101 and an outer end of the wiring member 103 is fixed to the housing 102.
The flexible wiring member 103 is a belt-like flexible printed circuit board (e.g. harness), for instance to connect electrical parts provided on the rotor 101 to other electric parts provided on the fixed housing 102, respectively through the conductive pattern of the electric wiring member 103.
Further, FIG. 1(a) shows a state where the electric wiring member 103 is full wound u counterclockwise around the rotor 101 by M turns in such a way as to be brought into close contact with the outer circumference of the rotor 101, and therefore only the outer end 103a of the wiring member 103 is connected to the fixed housing 102. In this state it is impossible to further wind up the rotor 101 counterclockwise relative. to the fixed housing 102. On the other hand, FIG. 1(b) shows a state where the electric wiring member 103 is full wound off clockwise around the rotor 101 by N turns in such a way as to be brought into close contact with the inner circumference of the fixed housing 102, and therefore only the inner end 103b of the wiring member 103 is connected to the rotor 101. In this state, it is impossible to further wind off the rotor 101 clockwise relative to the fixed housing 102.
In the prior-art device as described above, however, there exists a problem in that when the number of rotations of the rotor 101 is required to increase relative to the fixed housing 102, the length of the flexible wiring member 103 inevitably increases and therefore the flexible wiring member 103 increases both in electric resistance and cost.
In more detail, for example when the wiring member 103 is wound up around the rotor 101 counterclockwise by 3 turns and the rotor 101 is wound off clockwise by 1 turn, the number of remaining turns of the wiring member 103 around the rotor 101 is 2(=3-1). In general, when the wiring member 103 is wound up counterclockwise around the rotor 101 by M turns at the first and the rotor 101 is wound off clockwise by X turns, the number of remaining turns N of the wiring member 103 around the rotor 101 can be expressed as N=M-X.
Further, when the wiring member 103 is full wound off, the wiring member 103 is brought into tight contact with the inner circumference of the fixed housing 102. Therefore, if the number of the tight turns in the full wind-off condition is denoted as N, and the number of the tight turns in full wind-up condition is denoted as M, the required length L.sub.2 of the prior-art wiring member 103 can be roughly expressed as EQU L.sub.2 =.pi.d.sub.1 M=.pi.d.sub.2 N=.pi.d.sub.2 (M-X)
where d.sub.1 denotes the outer diameter of the rotor 101, and d.sub.2 denotes the inner diameter of the fixed housing 102. Therefore, EQU M={d.sub.2 /d.sub.2 -d.sub.1)}X
That is, L.sub.2 can be rewritten as EQU L.sub.2 =.pi.d.sub.1 {d.sub.2 /(d.sub.2 -d.sub.1)}X
To overcome the above-mentioned problems, Japanese published Examined (Koho) Patent Appli. No. 63-5519 discloses a structure such that planetary gears are provided so as to revolve around and in mesh with the rotor, and an electric wiring member is supported by a reel disposed coaxially with the planetary gears, in order to reduce the effective length of the flexible wiring member.
In this prior-art structure, however, since the middle portion of the electric wiring member is supported by the planetary reel, there exist various problems as follows: the wiring member tends to be bent at the middle portion; the wiring member is subject to damage; the flexibility and the durability of the wiring member itself deteriorate because the wiring member is wound up or off around a relatively small-diameter planetary reel; a higher load tends to be applied to the contact portion between the housing and the wiring member so that the connection between the two is not stable.